1. Field of the invention
The present invention relates to an x-ray tube for generating x-rays, an x-ray generator, and an inspection system for an object to be inspected using them.
2. Related Background Art
Known as a conventional x-ray tube is one incorporating therein an electron gun for emitting electrons and a target for generating x-rays in response to the electrons as described in Japanese Patent Application Laid-Open No. HEI 7-296751. On the other hand, known as a conventional x-ray generator is one incorporating therein an x-ray tube, a driving circuit for the x-ray tube, and the like as described in Japanese Patent Application Laid-Open No. HEI 7-29532.
Such x-ray tube and x-ray generator are mainly used for nondestructive/noncontact observation of internal structures of objects and the like as described in Japanese Patent Application Laid-Open No. HEI 6-315152. For example, an object to be inspected is irradiated with x-rays emitted from the x-ray tube and x-ray generator, and the x-rays transmitted through the object are detected by an x-ray/fluorescence multiplier (an image intensifier tube: I.I. tube) or the like. Then, the resulting magnified penetration image of the object is observed, whereby the nondestructive/noncontact observation of internal structure of object becomes possible.
In general, as described in Japanese Patent Application Laid-Open Nos. HEI 6-94650 and HEI 6-18450, such an inspection of the object to be inspected employs a technique in which the object is rotated about an axis orthogonal to the direction in which the x-rays are emitted, so as to change the orientation of the object, thereby accurately specifying a defective site.
On the other hand, the magnification rate of the penetration image is determined by the ratio between the distance (A) from the x-ray generating position (the focal position of the x-ray tube) within the x-ray tube apparatus to the position of the object and the distance (B) from the position of the object to the x-ray entrance surface of the I.I. tube. That is, the magnification rate M is expressed by
M=(A+B)/A.xe2x80x83xe2x80x83(1)
Normally, A less than  less than B, and therefore the expression (1) can be represented by
M=B/A.xe2x80x83xe2x80x83(2)
Namely, for yielding a greater magnification rate, decreasing A or increasing B may be considered. Increasing B, however, not only enhances the overall size of the x-ray inspection apparatus, but also remarkably increases its weight by requiring a greater amount of lead shield for keeping the x-rays from leaking outside, and so forth.
Therefore, it is desirable that Abe as small as possible. In the case using a technique in which the orientation of the object to be inspected is changed as mentioned above, however, a sample holder for mounting the object or the like may come into contact with the exit surface of the x-ray tube if A is made smaller. Consequently, there is a certain limit to increasing the magnification rate of penetration image. Hence, it has been difficult to accurately inspect the state of an object to be inspected while observing a penetration image thereof with a high magnification rate.
For overcoming problems such as those mentioned above, it is an object of the present invention to provide an x-ray tube, x-ray generator, and inspection system which can emit x-rays while objects to be inspected are disposed closer thereto.
The present invention provides an x-ray tube having a front end face with an x-ray emitting window, and a taper surface disposed near the emitting window of the front end face and tilted with respect to an x-ray emitting direction. Also, the present invention provides an x-ray tube in which two taper surfaces each mentioned above are symmetrically formed on both sides about the emitting window. Further, the present invention provides an x-ray tube in which the two taper surfaces are tilted by the same angle with respect to the x-ray emitting direction. Also,the present invention provides an x-ray tube employed in an inspection system which inspects a state of an object to be inspected by emitting an x-ray toward the object and detecting the x-ray transmitted through the object, the inspection system being capable of adjusting an orientation of the object about an axis intersecting an x-ray emitting direction, wherein the x-ray tube has an x-ray emitting window disposed at a front end face thereof facing the object, and a taper surface formed near the emitting window of the front end face and tilted with respect to an x-ray emitting direction while being parallel to the axis.
When these aspects of the invention are employed in an inspection system which inspects an internal structure of an object to be inspected and the like by irradiating the object with an x-ray and detecting the x-ray transmitted through the object, the taper surface formed therein can prevent the object from abutting against the front end face even if the object is pivoted about the axis intersecting the emitting direction while the object is disposed close to the x-ray emitting window. Therefore, while the object to be inspected is disposed close to the x-ray emitting position, the orientation of the object can be changed. As a consequence, not only a magnified penetration image of the object with a high magnification rate is obtained, but also the internal structure of the object and the like can be verified in detail while the orientation of the object is changed.
On the other hand, the present invention provides an x-ray generator comprising x-ray emitting means for emitting an x-ray, wherein the x-ray emitting means is any of the above-mentioned x-ray tubes. Also, the present invention provides an x-ray generator comprising x-ray emitting means for emitting an x-ray, the x-ray generator comprising a housing for accommodating a component, wherein a surface of the housing provided with an emitting window of the x-ray emitting means is formed with a taper surface tilted with respect to an x-ray emitting direction. Further, the present invention provides an x-ray generator in which the emitting window is disposed in a surface of the housing at a position lopsided to one side, and the taper surface is formed in the surface on the other side. Also, the present invention provides an x-ray generator in which two taper surfaces each mentioned above are symmetrically formed on both sides about the emitting window. Further, the present invention provides an x-ray generator in which the two taper surfaces are tilted with respect to the x-ray emitting direction by the same angle.
When these aspects of the invention are employed in an inspection system which inspects an internal structure of an object to be inspected and the like by irradiating the object with an x-ray and detecting the x-ray transmitted through the object, the taper surface formed therein can prevent the object from abutting against the front end face even if the object is pivoted about the axis intersecting the emitting direction while the object is disposed close to the x-ray emitting window. Therefore, while the object to be inspected is disposed close to the x-ray emitting position, the orientation of the object can be changed. As a consequence, not only a magnified penetration image of the object with a high magnification rate is obtained, but also the internal structure of the object and the like can be verified in detail while the orientation of the object is changed.
Also, the present invention provides an inspection system for inspecting a state of an object to be inspected by irradiating the object with an x-ray and detecting the x-ray transmitted through the object; the inspection system comprising any of the above-mentioned x-ray generators for emitting an x-ray; pivoting means for pivoting the object about an axis intersecting an x-ray emitting direction; and x-ray detecting means, disposed behind the object in the x-ray emitting direction, for detecting the x-ray transmitted through the object.
According to this aspect of the. invention, the taper surface formed therein can prevent the object from abutting against the front end face even if the object is pivoted about the axis intersecting the emitting direction while the object is disposed close to the x-ray emitting window. Therefore, while the object to be inspected is disposed close to the x-ray emitting position, the orientation of the object can be changed. As a consequence, not only a magnified penetration image of the object with a high magnification rate is obtained, but also the internal structure of the object and the like can be verified in detail while the orientation of the object is changed.